Why Offshore Windfarms are Underperforming

Posted: December 13, 2012 by tallbloke in solar system dynamics

From Reuters By Gerard Wynn:

Garrad Hassan’s report, “Offshore wind: Economies of scale, engineering resource and load factors”, sought to “provide a supported opinion on the likely load factors for offshore wind power in the UK Round 1 and 2 offshore wind farms”.

Government studies have since cited it as a reference.

The report calculated a range of load factors from 33 to 38 percent, for wind speeds ranging from 8.5 to 9.5 metres per second (See Chart 4).

Actual annual average load factors in fact only passed 35 percent for the first time last year, according to the Department of Energy and Climate Change’s (DECC) “Digest of United Kingdom Energy Statistics 2012”.

For previous years they were in the range 26-30 percent, or 28-35 percent depending on whether they are measured including or excluding turbines under construction.

DECC provided figures

DECC provided figures

More recent data show that load factors this year dipped back below the bottom end of the Garrad Hassan range.


A small variation in wind speeds significantly impacts the amount of electricity produced yet speeds have met expectations.

Historical data show that average British wind speeds have averaged around 9 metres per second since 2001, in the centre of the Garrad Hassan projections.

Those observed wind speeds are averaged for the whole of the UK, implying higher values for the superior offshore resource.

Other factors that will impact load factor include: downtime (as a result of technical faults and servicing); wake losses (from turbines caught in the wind “shadow” of others); and electrical transmission losses.

One possible culprit for the lower-than-expected load factors are wake losses.

UK-based renewable energy developer Renewable Energy Systems (RES) estimates that these have been under-estimated as a result of applying onshore wind modelling techniques to offshore farms.

“Research carried out on operational data of offshore wind farms has shown that the actual wake losses for large arrays of turbines are greater than what the industry standard onshore wake models predicted,” the company said in a presentation to an offshore wind conference last year.

RES reported actual wake losses several percentage points higher than as modelled using the “onshore method”.

It estimated actual wake losses for the Horns Rev offshore wind farm off Denmark at 12.4 percent compared with a modelled 8.3 percent, and similar discrepancies for Denmark’s Middelgrunden farm (10 percent versus 6.2 percent) and the Lillgrund farm between Denmark and Sweden (23 percent versus 14.7 percent).

Garrad Hassan’s 2003 report did not explain or reference its estimate for average British offshore wind farm wake losses of 8 percent of output.

Full story Here

  1. G. Watkins says:

    From the graphs, there seems to be little hope of on and off-shore windmills complementing each other despite the geographical spread. Why does hydro follow the wind generation and why show it at all?

  2. P.G. Sharrow says:

    Wind farms do not under perform. Salesmen over promise results! Wind farms are a con game to get subsidies. Cut off the subsidies and they will be scrapped. I have been involved in alternative energy systems for over 40 years. Large scale wind farms very rarely pencil out without special treatment. Only creative spread sheet calculations and subsidies, as well as outright lies, can make them appear to be a good deal. They also slow the surface winds and disrupt the climate.
    For the good of the World and lives of the people, cut the subsidies and scrap the wind farms. pg

  3. oldbrew says:

    Also the best sites are likely to be exploited first, meaning the averages will tend to fall later unless the technology (efficiency, reliability, etc.) improves sufficiently to counter that

  4. Simon says:

    Nothing to add of any value, but I like P.G. Sharrow’s expression “pencil out” in relation to the con game for subsidies and hope to be able to use it some time. Thanks.

  5. Brian H says:

    Large baseload wind (and for that matter solar) energy-harvesting installations suffer from numerous endemic and intractable and irreducible deficiencies: intrusive siting, massive material costs for initial installation, unknown but very high maintenance obligations, highly variable (uncontrollable) output profiles, transmission requirements from remote locales, unavoidable occasional zeroing of output due to both predicable and unanticipated external conditions, requiring complete standby backup — and more.

    “Further research” cannot mitigate these issues and problems. They are “endemic”, part of the package. Only if no other options were available would they be tackled by any rational actor.

    Or if there were some other, undisclosed, overriding agenda for doing so. Alarmingly, this appears to be the case, from both direct evidence and process of elimination.

  6. Hans Jelbring says:

    A very interesting economical report about real wind power performance is found at http://www.ref.org.uk/attachments/article/280/ref.hughes.19.12.12.pdf
    It does show and estimated the mostly forgotten importance of technical degradation of windfarms. Still it does not even mention the cost of the needed stand by power and incrreased grid costs that are big for the intermittent wind power energy as far as I understand in a quick read.

  7. tchannon says:

    Wearing an engineer hat, if the report is correct it is a damning the competence at all levels involved.

    I disagree about technology maturing, is far too new and small scale, on top of which it is in reality non-commercial by which I mean it is not done with hard brass at total risk to make a profit. This is an obvious dead duck, the alive know that, hence will not touch it.

    Electricity generation from wind is non-sustainable, the edge of the report.

    So we have a joke as a viable business and clear evidence of a non-viable business.
    A viable concern stands and walks on it’s own legs in perpetuity.

    Included in this is the blatantly obvious maintain, repair and replace. There is no outside money for replace. If it breaks fix it damn quick, money stops.

    Underneath all this is meddling with reality.